ATTINY25_09 Datasheet, PDF (18/196 Pages) ATMEL Corporation – 8-bit Microcontroller with 2/4/8K Bytes In-System Programmable Flash

5.3.6
5.3.7
5.3.8
5.3.9
Atomic Byte Programming
Using Atomic Byte Programming is the simplest mode. When writing a byte to the EEPROM, the
user must write the address into the EEAR Register and data into EEDR Register. If the EEPMn
bits are zero, writing EEPE (within four cycles after EEMPE is written) will trigger the erase/write
operation. Both the erase and write cycle are done in one operation and the total programming
time is given in Table 20-1. The EEPE bit remains set until the erase and write operations are
completed. While the device is busy with programming, it is not possible to do any other
EEPROM operations.
Split Byte Programming
It is possible to split the erase and write cycle in two different operations. This may be useful if
the system requires short access time for some limited period of time (typically if the power sup-
ply voltage falls). In order to take advantage of this method, it is required that the locations to be
written have been erased before the write operation. But since the erase and write operations
are split, it is possible to do the erase operations when the system allows doing time-critical
operations (typically after Power-up).
Erase
To erase a byte, the address must be written to EEAR. If the EEPMn bits are 0b01, writing the
EEPE (within four cycles after EEMPE is written) will trigger the erase operation only (program-
ming time is given in Table 20-1). The EEPE bit remains set until the erase operation completes.
While the device is busy programming, it is not possible to do any other EEPROM operations.
Write
To write a location, the user must write the address into EEAR and the data into EEDR. If the
EEPMn bits are 0b10, writing the EEPE (within four cycles after EEMPE is written) will trigger
the write operation only (programming time is given in Table 20-1). The EEPE bit remains set
until the write operation completes. If the location to be written has not been erased before write,
the data that is stored must be considered as lost. While the device is busy with programming, it
is not possible to do any other EEPROM operations.
The calibrated Oscillator is used to time the EEPROM accesses. Make sure the Oscillator fre-
quency is within the requirements described in “Oscillator Calibration Register – OSCCAL” on
page 26.
The following code examples show one assembly and one C function for erase, write, or atomic
write of the EEPROM. The examples assume that interrupts are controlled (e.g., by disabling
interrupts globally) so that no interrupts will occur during execution of these functions
18 ATtiny25/45/85
7598H–AVR–07/09